Two former Parramatta Eels players are accused of harbouring semi-automatic weapons and possessing more than half-a-million dollars in cash after dramatic arrests in Sydney's Centennial Park yesterday.

An academic study of Twitter opinions is pointing to a narrow defeat for the 'yes' vote in the same-sex marriage survey.

The study is at odds with myriad opinion polls showing the 'yes' vote could be as high as 60 per cent.

While 72 per cent of tweets favoured same-sex marriage, less than 15 per cent were sent by people over the age of 55, a Griffith University study shows.

Academics David Tuffley and Bela Stantic used advanced data analytics which they say have proven uncannily accurate at predicting the outcomes of hard-to-call polls, including the 2016 US presidential election.

They looked at the publicly available data from 458,565 tweets through October 2017.

On the face of it, when all the captured Tweets were considered, there appeared to be overwhelming support for 'yes', they said.

Taking the sentiment of the unique users into account, the adjusted figure in support came down to from 72 per to 57 per cent.